Arc melting processes for melting a metal material accommodated in a mold using heat energy of an arc are known conventionally and widely. The arc melting processes include a consumable electrode arc melting process and a non-consumable electrode arc melting process. Of these, the non-consumable electrode arc melting process is such that a tungsten electrode serves as a cathode using a direct-current arc power source in a pressure-reduced argon atmosphere, a direct-current arc is generated between the cathode and the metal material (anode) placed on a water-cooled mold, so that the metal material is melted with heat energy of the arc.
An example of a structure of a non-consumable electrode arc melting furnace of a conventional technology is shown in FIG. 13. In an arc melting furnace 200 as shown, a copper mold 201 is in close contact with a bottom of a melting chamber 210, so that the melting chamber 210 is an airtight container. Further, a tank 202 through which cooling water circulates is provided under the copper mold 201, so that the copper mold 201 is a water-cooled mold.
Further, as illustrated, a rod-like water-cooled electrode 203 is inserted into the chamber through an upper part of the melting chamber 210 and a tip portion made of tungsten as a cathode is arranged to be moved by operating a handle part 204 up and down, back and forth, and to the left and right in the melting chamber 210.
In the case where a metal is melted in this arc melting furnace 200 to obtain an alloy, weighted metal materials are first placed on the copper mold 201. After arranging the inside of the melting chamber 210 to be of an inert gas (usually argon gas), arc electric discharge is generated between the tungsten electrode (cathode) of the water-cooled electrode 203 and the metal material on the copper mold 201 (anode), so that a plurality of different metal materials are melted and alloyed by the heat energy of the discharge.
Incidentally, in an alloy generating process using the arc melting furnace as described above, a metal having a large specific weight is easy to collect at the bottom of alloyed materials. Thus, it is necessary to thoroughly stir the alloy when the alloy is in a melted state in order to generate an alloy of good quality.
However, the molten bottom which is in contact with the mold is cooled, since the metal materials are melted on the water-cooled mold. There is, therefore, a technical problem in that the molten metal located at the bottom changes from liquid phase to solid phase immediately, and sufficient stir cannot be performed.
Then, conventionally, in order to solve the above-mentioned problem, a method has been used in such a way that after cooling an alloy material M which is melted, the material M is turned over on the copper mold 201 with a turning bar 205 which is operated from the outside of the melting chamber 210 as shown in FIG. 14 and melted again, and subsequently the process of cooling, turning, and melting is repeated a plurality of times to knead and alloy the material M. It should be noted that the arc melting furnace as described above is disclosed in Japanese Patent Application Publication No. 2007-160385.